Abstract
We present Atacama Large Millimeter/submillimeter Array (ALMA) 870$\mu$m
observations of 29 Herschel-selected submillimeter galaxies (SMGs) near QSO
sightlines. We detect a total of 39 sources with 870$\mu$m flux densities
between $0.7 < S_870 < 15$ mJy in 27 of the 29 fields. Ten Herschel sources
have multiple ALMA counterparts. The intrinsic source sizes range between 0.2"
and 0.7", with a mean at $0.29\pm0.03$ arcsec. The Herschel-QSO separations for
six of the pairs are less than 10", comparable to the sizes of the Herschel
beam. We find that four of these six Herschel-detected QSOs are embedded in
SMGs with $3.0 S_870 14.2$ mJy, although the rest-frame ultraviolet
spectra of the QSOs show no evidence of significant reddening. No additional
mJy-level submillimeter companions are detected around these QSOs. Black hole
accretion and star formation contribute almost equally in bolometric luminosity
in these galaxies. The SMGs hosting QSOs show similar source sizes, dust
surface densities, and SFR surface densities as other SMGs in the sample. We
find that the black holes are growing $\sim$3$\times$ faster than the galaxies
when compared to the present-day black-hole-galaxy mass ratio, suggesting a QSO
duty cycle of $łesssim$30% in SMGs at $z 3$. The remaining two
Herschel-detected QSOs are undetected at 870$\mu$m but each has a bright
submillimeter "companion" only 9" and 12" away (71 and 95 kpc at z = 3). They
could be either merging or projected pairs. If the former, they would represent
a rare class of "wet-dry" mergers. If the latter, the QSOs would, for the first
time, probe the circumgalactic medium of SMGs at impact parameters below 100
kpc.
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